Regional hyperthermia: a clinical appraisal of noninvasive deep-heating methods

The concentric single-turn self-resonant coil operated at 13.56 MHz (CC) and the annular array applicator (AA) operated at 55 to 100 MHz are the only regional heating devices the clinical use of which has been subjected to sufficient thermometric characterization to be evaluable. The clinical heating characteristics and toxicity of both devices are reviewed. When spatial temperature measurements have been made during clinical treatments with the CC, the observed temperatures have been consistent with theoretical predictions and phantom studies; temperatures fall with increasing radial depth, and potentially injurious heating in superficial normal tissues and ineffective heating in deep-seated tumor loci have been commonly observed. The CC is ineffective in heating central pelvic tumors due to inadequate penetration and power-limiting sacrococcygeal pain. The AA has been demonstrated to heat many deep pelvic tumors to maximum temperatures greater than 42-43 degrees without significant side effects, but further study is needed to determine the feasibility of achieving higher minimum tumor temperatures and longer treatment durations. In the upper abdomen, the AA appears to have a slight superiority in rapid tumor heating at depth, but both devices have major limitations with insufficient penetration (CC) or treatment limiting systemic heating (AA). There has been no adequately thermometrically documented experience with heating in the deep thorax with either device.